The present invention relates to semiconductor devices and more particularly to III-nitride semiconductor devices and methods of fabricating III-nitride semiconductor devices.
A III-V semiconductor is a semiconductor material that is composed of a group III element and a group V element. III-V semiconductors are desirable for power applications, but have not been exploited extensively due in part to difficulties in fabrication.
For example, one commercially desirable III-V semiconductor is III-nitride. Note that as used herein III-nitride semiconductor or GaN-based semiconductor refers to a semiconductor alloy from the InAlGaN system. Examples of alloys from the InAlGaN system include GaN, AlGaN, AlN, InN, InGaN, and InAlGaN. Note that while nitrogen is present in each alloy, the presence and proportion of In, Al, or Ga can be varied to obtain an alloy in the InAlGaN system.
III-nitride semiconductor devices are desirable for power applications due in large part to the high band gap of III-nitride semiconductor materials. To fabricate a III-nitride semiconductor device at least one III-nitride semiconductor alloy (i.e. an alloy from the InAlGaN system) needs to be formed over a substrate. The three well known substrate materials for III-nitride semiconductor devices are sapphire, SiC and Si.
Silicon substrates are more desirable commercially because of low cost, and high thermal conductivity. However, due to lattice mismatch and differences in the thermal expansion characteristics of III-nitride semiconductor alloys and silicon, thick III-nitride semiconductor layers (e.g. more than 1 micron thick) either crack or cause the silicon wafer to bend. It should be noted that the cracking problem associated with thick III-nitride semiconductor layers is not experienced only when a silicon substrate is used, and thus the problem is not limited to III-nitride semiconductor that is formed on silicon substrates.